Radio based communication systems are known. Such systems typically transmit and receive on an assigned frequency pair or on a single frequency in a TDM format. The assigned frequency or frequency pair may be selected either by the user or, in the case of a trunked system, assigned by a system controller. Other radio communication systems transmit from radio-to-radio on a single frequency in a simplex mode.
For increased flexibility radio communication units are often constructed to operate from portable battery power sources. The use of light-weight battery power sources has contributed to the utility of hand-held portables.
Batteries, while providing the greatest mobility, also suffer from disadvantages associated with limited, and sometimes unpredictable, operational life. Factors affecting battery life include transmitting time as well as time spent monitoring incoming messages.
While significant battery power is required by a radio transmitting a message, more total radio time (and resultant battery capacity) may be consumed monitoring for incoming messages. A radio operator, in most cases, is not able to schedule communication transactions. A radio, consequently, must remain in an activated state, monitoring for incoming signals, during relatively long periods of inactivity.
Since the utility of a two-way portable radio lies in its ability to transmit and receive messages, the utility of a radio is increased by extending the period between battery replacement by conserving battery capacity. Accordingly, a need exists for a method to conserve battery capacity while monitoring for messages without interfering with radio operation.